Method and apparatus for producing chorus effects in music



Sept. 22,

METHOD AND APPARATUS FOR PRODUCING CHORUS EFFECTS IN MUSIC Filed April 2'7, 1951 BOUECE OF MOUULATING VIBRATO J. M. HANERT PHASE 0' FIRST AUDIO FREQUENCY OSCILLATOR 'A' OF NOMlNAL MUSICAL PITCH 1,. ,A=44O :b 0-5 70 FEEQUENCY sreNALs OF OPPOSITE PHASES 0 AND 150"? (FM-,- 2)

' PHASE mo 7 NOMINAL MUSICAL PITCH (FIG. 5 02 5a) SECOND AUDIO FREQUENCY 12 Sheets-Sheet 1 COM MON OUTPUT SYSTEM OSCJLLATOFZ "5 OF A: 440 057 (Fl(;1.5 02 5a) souzce OF FREQUENCY AUDIO FREQUEHNHCY OSCILLATOR A OF NOMINAL MU5ICAL PITCH MODULATIO 5\C1NALS OF DIFFERENT FZEQUENCKES .0. .g. 4AND Ag. A=44o :t 0.5 "la FIG 5 02 3a) (FIG. 2A)

AUDK) FnzeQug cY OSCILLATOR 5 OF NOMINAL MUSICAL PITCH Lg, =44o 3:057

COMMON OUTPUT SYSTEM Sept. 22, 1959 J. M. HANERT 2,905,040

METHOD AND APPARATUS FOR PRODUCING CHORUS EFFECTS IN MUSIC Filed April 2'7, 1951 12 Sheets-Sheet 2 6+ 5+ (90a 455w -4.5v A 6 210" 4) 1 cam Sept. 22, 1959 J. M. HANERT METHOD AND APPARATUS FOR PRODUCING CHORUS EFFECTS IN MUSIC 12 Sheets-Sheet 5 Filed April 27, 1951 FHZST OF SEVERAL CASCADED STAGES OF FREQUENCY DIVIDEZS OSCILLATOR OF MELODYJISISTRUMENT --TONIE o- QUALITY CONTROLS Q 0- oPOWEE AMPLlFiEK IN oCLUDlNC: VOLUME CONTROL ohm/WWW w I f if 4 27 all/WW 7 Sept. 22, 1959 T T l l9 (150 1 J. M. HAN ERT METHOD AND APPARATUS FOR PRODUCING CHORUS EFFECTS IN MUSI C Filed April 27, 1951 12 Sheets-Sheet 4 22 0 220 v|BF 2ATo g MELODY SECTION 5 POWER AMPLIFIER & APPARATUS 159 SHOWN m F|e..4 INCLUDING voLuMe SHOWN IN CONTROLLED BY 3 CONTROL O QFIHZ MANUAL OF o2c=AN 2Z2 12 m) i E. 25! 240 25V ONE MANUAL zaAN (F), PEEAM- 5ECT|ON 57 O5C1LLATOR5 2 PLIFIEK A5 SHOWN m FIG.5OE F\e..5a 5 239 LO Q Q,VTE2M\NAL. OF ALL (94-) osclLLATozs Q 2245 6\/ 1 6+ VIBFZATO a APPARATUS /I2l (I80 d SHOWN m FIG- 2 L J /zz(o) V V v v. v

OSCIL- osuL- O5C.lL- OSCIL- 05.-

LATOIZ LATOR LATOR LATora LATorz F02 IST- FOR ZND- F02 5120. F02 4TH. FOR 5TH- OCTAVE OCTAVE ocTAvE OCTAVE OCTAVE L x l l 1 MANUAL- CONT2OL5-AMPLIFIE6Z AND, SPEAKER zso j 6 COMMON MANUAL i 09(16049 1 E OD T 0 1 2: 0AM IL N APPARATUS L 5 COMMON SHOWN m I592 OUTPUT FIG-Z f SYSTEM 1 2ND. MELODY SECTION /2o(o4 SHOWN lN F-(6-4 Sept. 22, 1959 HANERT 2,905,040

METHOD AND APPARATUS FOR PRODUCING CHORUS EFFECTS IN MUSIC Filed April 27, 1951 12 Sheets-Sheet 6 MASTER CASCADED 05cm.- FREQUENCY LATORS mvloeszs MANUALS FEDALS EAMPLIFI TONE QUALITY H9 |80 AND V 4)) VOLUME VBEATO CONTROLS AzATus SHOWN W Flag REvEiZea ERATION 120( b) CONTIZOL.

POWER I89 AMPLIFIER AND SPEAKER Sept. 22, 1959 HANERT 2,905,040

METHOD AND APPARATUS FOR PRODUCING CHORUS EFFECTS IN MUSIC Filed April 27, 1951 12 Sheets-Sheet '7 1ST (LOWE5T) 2ND. 520 4TH. 5TH- 6TH- ocTAvEs OCTAVES ocrAvEs OCTAVES OCTAVES OCTAVES SALICIONAL r-h r31 1"11 Fi r 124 4 l VIOLIN [:El [:3 i l i [3] limp GENEQATOES OF TONE 5l6NALS USED MOSTLY ON LOWER MANUAL (O) a O c OPEN DIAPASON :21 Ji 6 m? g HAIZMONIC. FLUTE k /21 1' i mac 5 /Z5\T90-) 5 0 j DULCJANA M64 1 x 8 pp ZMMMJfamJ/ii Sept. 22 1959 J. M. HANERT METHOD AND APPARATUS FOR PRODUCING CHORUS EFFECTS IN MUSIC 12 Sheets-Sheet 9 Filed April 27, 1951 H MPH nu Sept. 22, 1959 J. M. HANERT 2,905,040

METHOD AND APPARATUS FOR PRODUCING CHORUS EFFECTS m MUSIC FiledApril 2'7, 1951 Y 12 Sheets-Sheet 10 MELODY TONE TONE a COUPLER GENERATOR VOLUME FIG-4 CONTROLS w swn'cu UPPER MECHANISM z5 4 MANUAL COUPLER 42 0 1270201) 392 L. SWITCH MECHANISM F 6 TONE & Y 585 EENEEATozs VOLUME 3 FIG-5 02 5G CONTROLS COUPLER 582 584 VOLUME ggzgs 'g 7( 0%) 'comzoz. g LOWER T T M 2 AMPLIFKEIZ MANUAL COUPLER TONE 2,

5WITCH/ GENERATORS VOLUME MECHANlSM 4 masozag CONTROLS 5 V7 secomo TONE 5IC-ANAL FzoM souzce 5 (|&o d

NSTANTANEOUS FREQLILENCY 1/7 SECOND VIBRATO PHASE v| EEATo PHASE lzo \NSTANTANEOUS iREQliENCY U 4 h o g u ll 1 FREQUENCY INSTANTANEOUS V4 sa co N 0 f Se t. 22, 1959 J. M. HANERT METHOD AND APPARATUS FOR PRODUCING CHORUS EFFECTS IN MUSIC Filed April 27, 1951 12 Sheets-Sheet 11 SOURCE OF ELECTRICAL 5I6NALS DEFlCIENT IN VIBZATO ORGAN KEYBOARD MELODY SECTION 5HOWN IN Pic-1.4-

MUSICAL TONE AND CHORUS AMPLlFlEIZ POWER 0 TAMPLIFIEE AMPLIFIER AND AlZTlFIClAL LINE Sept. 22, 1959 J. M. HANERT METHOD AND APPARATUS FOR PRODUCING CHORUS EFFECTS IN MUSIC Filed April 27 1951 12 Sheets-Sheet 12 AMPLIFIER o I I \I 'I V 5UPER A. F- ,4 47.9 n 475 -464 OSCILLATOR A.F.5|C:NAL. 47o

. e 486 ,5 sow-2c, k 466 4 AMPLIFIER:

United States Patent METHOD AND APPARATUS FOR PRODUCING CHORUS EFFECTS IN MUSIC John M. Hanert, Park Ridge, Ill., assignor to Hammond Organ Company, a corporation of Delaware Application April 27, 1951, Serial No. 223,376 21 Claims. (Cl. 84--1.24)

My invention relates to electrical musical instruments and more specifically to a novel means and method for producing the effect of a large chorus of instruments.

One of the most important and frequently-used musical or tonal effects is that of mass or chorus, as produced by a large number of musicians or tone producing instrumentalities playing or sounding in unison, for example, the first violin section of a symphony orchestra, or the many 8 ft. stops which may be simultaneously drawn on a large pipe organ. If these many tonal sources were exactly in tune, there would be no chorus effect and much of the musical charm resulting therefrom would be lost. It invariably happens, however, that the many musicians are unable to play exactly in tune and, in the case of the large organ, the many pipes are slightly out of tune with respect to each other. The highly desirable chorus effect is produced by these unavoidable small differences in pitch.

In an electrical musical instrument, the cost of the tone generating equipment is a substantial portion of the total cost of the instrument. in most instances, the provision of a large number of slightly detuned chorus generators is impractical and prohibitive in cost. This problem of generating chorus tones is an old one and many attempts have been made to solve it. One method has been to provide two or three slightly detuned tone-gem crating gsources for each note of the scale, as shown, for example in Patent No. 2,159,505. Experience has shown, however, that when such a small number of chorus generators is provided,, the effect produced must correspond to a relatively narrow and restricted chorus band.

Another effect has been obtained in organs by providing an intensity tremulant which, upon mathematical analysis, may be thought of as being productive of a chorus of side-band frequencies, as shown in Patent No. 1,956,350. However, this effect is not very satisfactory because the listeners ear does not acoustically interpret the phenomenon as being a chorus, but rather as an obtrusive and unmusical volume shake in the music.

Still another method has been to cause an over-all frequency or pitch modulation (vibrato) in the instrument, for example, as disclosed in my prior Patents Nos. 2,254,- 284 and 2,382,413. While these vibrato or frequency modulation systems result in tones which are far less obtrusive than the tremolo, because the energy of the tone is relatively constant, they nevertheless have the disadvantage that the discerning listener can easily hear the pitch of the tones rise and fall at the vibrato rate. In the true chorus effect, the energy as well as the pitch of the tones are perceived by the listener as being relatively constant.

An improved application of the vibrato principle to electrical musical instruments is disclosed in the patent to Laurens Hammond No. 2,276,389 wherein six different sources of vibrato modulating frequencies were employed in order to render the beat rate less obtrusive as the twelve successive semitones in the musical scale were sounded. Thus, for example, in the instrument shown in said patent "ice duce any recognizable chorus effect over and above the' condition where a unitary vibrato is employed on all the notes.

In the musical instrument of my invention, the illusion of a large chorus of players is created through a novel and simple acoustical principle. Briefly stated, this principle consists in causing electrical tone signal sources of substantially tthe same frequency (either as the fundamental or as a harmonic) to be provided with vibratos of opposite polarity or phase, so that as one source is modulated to a frequency above its nominal or average frequency, the other source will be simultaneously modulated to a frequency below the average frequency. When listening to both sources, the ear does not notice a change in frequency (as is the case with vibrato) because the average frequency of the tone is substantiailly constant. Since the energy in the output of each generator may be made to be relatively constant, there is no over-all tremulant effect in the tones of the instrument. If. an oscilloscope is used in studying the superposition phenomenon which occurs upon combining two waves of the same or approximately the same frequency but of opposite vibrato polarity, one can observe a very complicated unsteadiness in the intensity envelope of the output signal. This unsteadiness in intensity is a characteristic of the chorus tone and occurs whenever the outputs of two or more tone generators having slightly differing frequencies are superimposed.

To produce a maximum chorus effect in a musical instrument, it should have two complex wave tone signal generators having the same fundamental frequency available for each note of the musical scale and a means for vibrato frequency-modulating each of these tone generators with opposing polarities. However, the chorus principle of this invention may also be applied with excellent results to instruments where there is but a single complex wave generator for each of the notes of the scale. In these instruments the even-numbered harmonics of the lower pitch are also generated as the fundamental and harmonics of the note one octave higher in the scale. If the vibrato for the lower note generator is made to be of opposite polarity, or out of phase with respect to the vibrato for the generator having a pitch one octave higher, a very pleasing chorus effect is produced when these octavely-related generators are simultaneously sounded.

From the above it is seen that the primary object of my invention resides in producing the effect of a tonal chorus by frequency-modulating generators of substantially tthe same or octavely-related fundamental pitches in an opposing sense during a substantial portion of their modulation period.

A further object of the invention is to provide an improved electrical musical instrument capable of producing a desirable chorus effect from two tone signal sources of the same pitch by causing the sources to have oppositely phased vibratos.

A further object of the invention is to provide an improved electrical musical instrument in which several vibrato signals of different frequency, but within the vibrato range, are impressed upon different groups of generators of an electrical musical instrument, and thereby produce a desirable chorus effect.

A further object is to provide an electronic organ in which there are fewer oscillators than playing keys in the manual and in which the chorus effect is obtained by applying oppositely phased vibrato controlling frequencies to alternate octaves of oscillators.

A further object is to provide an improved electrical musical instrument employing oscillators as sources of tonesignals and to apply vibrato determining signals of different phases to successive octaves of. oscillators, so that, when playing in octaves, the second harmonic of the lower pitched tone will have its vibrato out of phase with respect to that of the fundamental of the higher pitched octave tone and thereby produce achorus effect.

Other objects will appear from the following description, reference being had to the accompanying drawings inwhich:

Figure 1 is ablock diagram illustrating one of the fundamental principles of the invention;

Figure 1a is a block diagram illustrating a secondary principle of the invention;

Figure 2 isa schematic wiring diagram of an apparatus for, producing vibrato signals of the same frequency but Of differentphases;

Figure 2a is a schematic block diagram of an apparatus for producing frequency modulating signals of different frequencies;

Figures 3 and 3a are schematic wiring diagrams ofoscillators which may be employed in the various types of electrical musical instruments shown in other figures of the drawings;

Figure 4 is a schematic wiring diagram of a representative portionof a melody section of an electrical musical instrument of the type which may be used as a part of instruments shown in other figures of the drawings;

Figure 5 is a partly block and diagram of an embodiment of the invention organ-section and a melody section;

Figure 6 is a block diagram of a single manualelec: tronic organ showing the application of my invention thereto;

Figure 7 is a block diagram of an electronic melody instrument or section of an instrument illustrating the manner in which my invention may be applied thereto;

Figure 8 is a partly block and partly schematic wiring diagram of a two manual organ employing oscillators as tone sources and illustrating the manner of utilizing the present invention therewith;

Figure 9 is a block diagram of an electronic organ having two sets of master oscillators for producing the chorus effect and showing the manner in which my invention isapplied thereto;

Figure 10 is.a block diagram of a two manual multiranksignal source in which the invention may be used therewith;

Figure 11 is a block diagram showing the manner in which vibrato controlling signals of different periodicity may be applied to an electronic organto produce the chorus effect;

Figure 12 is a similar block diagram showing the mannor in which two sources of vibrato frequencies of different periodicity may be applied to a single manual electronic organ to produce the chorus effect;

Figure 13 is in part a block and in part a schematic wiring diagram of an electronic organ having tone signal generating oscillators each operable at any one of four different, pitches, and in which keying circuits are provided so that two signals, of the same pitch but of differently phased vibrators, are transmitted-to the output system upon playing. a single key;

Figure 14 is a block diagram illustrating the manner in Whichthe invention may be applied to a two manual organ employing continuously operating oscillators as its tone, signal generators; 0

Figure 15 is a diagram illustratingthe principles underlying the-invention as .it is applied to two tone signal sources;

Figure.- 16 is adiagram to illustrate the manner of employing an partly schematic wiring r electronic organ illustrating the manner applying the invention to a musical instrument in which there are three different tone signal sources;

Figure 17 is a diagram to illustrate the manner in which a limited chorus effect may be obtained by fre quency modulating the tone signals at different vibrato rates;

Figure 18 is a schematic block and wiring diagram of an additional modification of the invention;

Figure 19 is a similar diagram showinga further modification of the invention; and

Figure 20 is a schematic block and wiring diagram showing how the inventionmay be employed and systems employing recorders and reproducers.

The invention now to be described in detail is of a fundamental character and iscapable of embodiment in a large number of different forms, and it has not been attempted to illustrate in detail how the invention may be used in all its possible ramifications, but instead, typical applications of the principles of the invention to representative types ofv musical instruments are herein described and illustrated.

The general character of the invention may best be described by reference to Fig. l in which there is a source 200E modulating vibrato frequency signals of opposite phases, indicated as 0 and The apparatus represented bythe block 20 is shown in Fig. 2 and will hereinafter be described in, detail. Boxes 21 and 22 each represent an audio frequency source, for example, oscillators A and B generating complex tone signalsof the samenominal musical pitch, assumed to be A=440, $0.3 percent. The term nominal musical pitch is used herein to mean a pitch which is closely associated with a particular note of the even tempered musical scale, and having a fundamental and harmonics in the audio frequency range extending from 32 c.p.s. to 15,000 c.p.s. In practice the exact fundamental frequencies of the notes generated in the organ may drift considerably from theirtheoretically accurate pitch and, in fact, such deviations or inaccuracies in relative pitch are conducive to remove the unwanted locking in frequency effect which otherwise may occur between unisons. (tones of the same nominal pitch), as well as between octavely related tone signal generators of complex wave form having low order integrally related-fundamental frequencies.

A tonev signal is complex when its low order harmonies are sufficient amplitude so that when the signal is translated into sound the harmonics have a readily noticeable effect on the quality of the tone as perceived by the listener. These two oscillators are independent in the sense that the frequency of one does not control that of the other and may be ofany suitable form, for example, of the type shown in Fig. 3 and hereinafter described- As will be described later with reference to Fig. 2 the. vibrato frequency signals provided by the apparatus 20-are of various phases, including 0 phase and 180 phase. The outputs of the oscillators are supplied to a common output system 23 which may include a speaker- 25. Merely for purpose of illustration the oscillator A has its vibrato determined by the vibrato signal source 20 in the 0 phase whereas the oscillator B is provided with a switch 24 which when in full line position supplies the vibrato modulating frequency to the oscillator B at 180? phase and when in dotted line position supplies theoscillator B with zero phase vibrato signal. Assuming thatthe switch 24 is in dotted line position the frequency of the signals produced by oscillators A and B will rise and fall together, at the same vibrato rate and to the same extent.

If the two sources 21 and 22 are exactly in tune, and generate pulsesin-phase with each other, the effect of combining them is merely to cause an increase in intensity. If the twooscillators A and B happen to be slightly out of-tune with respect to each other, the results of combining them are the same except for the addition of a slow phase-shifting efiect as they beatin and out of phase with each other. Depending upon their instantaneous relative phase, the resulting tone quality of-the combined oscillator outputs will be heard to vary slowly over a wide range. At times, the combination tone will even sound at the interval of the octave (if the generators produce pulses of like polarity) or will pass through a period of silence (if the generators produce pulses of opposite polarity). Introduction of a vibrato of like polarity in the tones of the two generators is found to have no beneficial effect whatsoever on this difference beat phenomenon, but rather tends to magnify the effect and produces a most unnatural whining effect. This whining effect is unmusical because it has a peculiar unsteady effect which suggests the sound heard over short-wave radio when listening to stations at great distances over changing sky wave paths. This whining effect is also heard to a lesser, but nevertheless disturbing, extent when tones, having vibratos of like polarity, an octave apart are played.

If, however, switch 24 is moved to its full line position so that the modulating vibrato frequency is impressed upon oscillators A and B in opposite phase, an entirely different and novel effect is obtained. The tone signals from the two oscillators will then vary in frequency in the manner indicated in Fig. 15, that is, one of the oscillators will be generating a frequency higher than the nominal frequency while the other oscillator is generating a frequency lower than the nominal frequency. In Fig. 15 the shape of the curves 26 and 28 is not of particular significance. The modulating frequency may be of a' sine Wave form or square wave form or any intermediate form. It will be understood that the curves 26 and 28 indicate merely the instantaneous frequencies of the oscillators A and B respectively.

When the vibrato frequencies applied to the oscillators A and B are of opposite phase or polarity, this undesirable whining effect disappears and a most realistic and musically attractive illusion of a chorus of instruments is produced. The pleasant tonal animation makes it almost impossible to perceive the beat caused by the difference in the average pitch of the two generators. This desirable masking of the difference beat is so great that it becomes virtually impossible to tune the oscillators to the same pitch while the chorus phenomenon is being produced. The extent of the chorus effect is controlled chiefly by the extent of the vibrato.

The reason for the disappearance of the whining effect lies in the fact that the two oscillators are always being frequency-modulated in opposite senses which makes it impossible for them to remain in any particular phase relation for a period of time more than a fraction of the vibrato period. It is interesting to note that the rate of the vibrato in the tones generated by the two sources may be varied without the listener being particularly aware of any change. Thus, the vibrato is being used purely as a means or mechanism for maintaining an illusion of chorus when the two tone generators are simultaneously sounded.

Assuming that the oscillators A and B are generators of complex tone signals, the frequencies of their harmonics will vary in the same manner as the frequencies of their fundamentals so that the chorus effect is present in all of the partials as well as in the fundamental.

The effect of moving the switch from its dotted line to its full line position is startling. In the dotted line position one hears what appears to be but a single tone signal source modulated by a vibrato frequency and if the sources are not of exactly the same frequency the above mentioned whining effect will be present, whereas, with the switch 24 in the full line position, one hears what is apparently a very large number of signal sources sounding simultaneously, namely, a full chorus and the vibrato effect is hardly noticeable. By constructing a simple apparatus of the type shown in Fig. l the musical 6 desirability and value of the chorus elfect may be demonstrated.

This chorus effect may be obtained by frequency modulating the two tone signal sources at different rates as diagrammatically illustrated in Fig. 1a. This method, however, is only about half as efiicient as that described above. In Fig. la it is assumed that the oscillators 21 and 22, the output system 23, speaker 25, and switch 24 are of the character above described with reference to Fig. 1.

The source of modulation signals 20A is, in fact, two sources of different frequencies, for example, 4 and 8 c.p.s., this apparatus being shown in detail in Fig. 2a. When the switch 24 is in its dotted line position the same non-chorus effects will be obtained as described under the corresponding condition with reference to Fig. 1. However, when the switch 24 is moved to its full line position the two oscillators will be frequency modulated in the manner represented in Fig. 17 wherein the dash line curve 26A represents the instantaneous fre quency of the output of the oscillator A while the full line curve 28A represents the instantaneous frequency of the oscillator B. For the particular modulating frequencies selected for illustration, the chorus pattern repeats four times per second. The chorus elfect is better if the modulating frequencies do not have a common integral factor (other than 1) e.g. 5 and 7 c.p.s. so that the chorus pattern repeats every second.

From Fig. 17 it will be apparent that the two oscillators have their frequency modulation of opposite polarity during only one half of the time, while during the remaining half time they are of the same polarity. Thus the chorus effect is obtained during only half the time that the tone is sounded, that is, during the time intervals indicated by the double headed arrows A and B. This method of frequency modulation produces results which are a substantial improvement over those of the prior art with respect to the simulation of a chorus. The frequency modulating rates 4 and 8 were selected because of the simplicity of the diagram of instantaneous frequencies (Fig. 17) but other modulating frequencies may be employed, the more desirable modulating frequencies lying within the range of from 3 to 10 c.p.s. Higher modulating frequencies, such as high as 15 c.p.s. may be used, but to most persons the chorus effect becomes less desirable. The diagram of Figs. 1a and 17 thus further illustrate the breadth of the fundamental principle of the invention.

As previously indicated, the invention may be embodied in a wide variety of musical instruments, and some of the different possible forms of instruments in which the invention may be utilized are illustrated in the drawings.

In general, most of these instruments. employ one or more oscillators which may be of any well-known type but which preferably are of the type shown in Fig. 3, or of the type shown in Fig. 3a. In Fig. 3 the oscillator comprises a triode 30 having an adjustable tuning circuit including a capacitor C32 and a variable inductance L34 connected between a terminal S and a terminal 36. The terminal 36 is connected to the control grid 38 of triode 30 through a capacitor C40. The cathode 42 is connected to a tap on the inductance L34 while plate 44 is connected to a terminal K through an attack resistor R46 which has a resistor R48 and capacitor C50 in series across its terminals. The plate 44 is connected to ground through an attack capacitor C52. The control grid 38 is connected to a terminal V through a decoupling resistor R54 while the terminal 36 is connected to a decoupling resistor R56 to a terminal F.

The terminal V will be connected to one of the terminals 121, 122, 124 to 127 of the vibrato apparatus (Fig. 2) depending upon the manner in which the oscillator is to be used, as will appear hereinafter.

The frequency of oscillation of the oscillator 30 may be decreased three semitones by connecting a capacitor C58 between the cathode and terminal S and for this reason the capacitor C58 is shown as connected between cathode 42 and a first tuning terminal T1 so that by a switching means, not shown in Fig. 3, T1 maybe connected to S whenever it is desired to lower the pitch of the oscillator by three semitones. In a similar manner the pitch of the oscillator may be lowered a full tone by connecting a capacitor C60 in series with CS8 by connecting a terminal T2 to the terminal S. The pitch of the oscillator may be lowered one semitone by connecting a third capacitor C62 in series with C58 and C60, this being accomplished by connecting a terminal T3 to the terminal S.

The oscillator shown is adapted to be'keyed (rendered operative) by supplying plate voltage to the terminal K and Will have its frequency shifted to introduce the vibrato effect by having a vibrato frequency signal impressed upon the terminal V. The signal which appears upon the terminal F is of flute-like character, that is, it is substantially sinusoidal. On the other hand, the signal appearing at the terminal S will be very complex and rich in harmonics so that, by the use of suitable filtering meshes, tone qualities of the string and reed families may be derived therefrom.

In such forms of the invention in which the signal is to be keyed, requiring a continuously operating tone signal generator, the oscillator shown in Fig. 3a may be employed. This oscillator comprises a triode 70, the control grid of which is connected to the V (vibrato) terminal through grid resistor R54.

The plate of the triode 70 is connected to ground through a filtering capacitor C53 and is connected to a 8-}- terminal through a load resistor R72. The cathode 74 is connected to a tap on a variable inductance L76 which has a capacitor C78 in parallel therewith. One end of the resonant circuit provided by L76 and C78 is connected to the grid of the triode 70 through a capacitor C80. The other terminal of the resonant circuit is connected to ground through a resistor R82 which has a resistor R84 in series with a capacitor C86 in parallel therewith. A secondary winding L88 is coupled to the inductance L76 and is connected between ground and a terminal F1 to provide a tone signal of flute-like quality. The string-quality signal is derived from a terminal S1 which is connected to the junction of C86 and R84.

The apparatus for producing vibrato modulating frequencies of several different phases is shown in Fig. 2

as comprising a phase shift oscillator 90 consisting of a triode 92 the cathode of which is connected to ground and the plate of which is connected to a 13+ terminal of the power supply through a load resistor R94. A multi section phase shifting mesh is connected between the plate and grid of the triode 92 and comprises a plurality of series capacitors C96, and shunt resistors R98. Each of the resistors has one end connected to a 2.5 v. terminal and its other end connected to one of the junctions between capacitors C96. This phase shifting mesh has terminals 100 to 105 at which the signal appears in different phases. Terminal 105 is connected to the grid of triode 92 by a resistor R106. Assuming that the phase of the signal produced by the oscillator 90 is at its plate and at the terminal 100, the phase of the signal at the terminal 101 will be 60, that at terminal 102 will be 90, and that a terminal 103 will be 120.

In order to amplify and produce several signals of different phases from the signal appearing at terminal 100, the latter is connected through a decoupling resistor R108 with the grid of a switching triode 110. This triode is supplied with plate current through a suitable load resistor R111 connected to a 13+ terminal. The cathode of triode 110 is connected to a 4.5 v. terminal by resistor R112 having a bypass capacitor C114 in parallel therewith. The plate of triode 110 is connected to a terminal 119 and the phase of .the signal appearing at this terminal is, of course, oppositeto that on the grid of the triode 110, namely, 180. The signal on the cathodeis, of course, of the same phase as that on the grid and this signal of 0 phase thus appears upon a terminal 122 connected to the cathode of triode 110.

A triode 116 has its input circuit coupled to the plate circuit of triode through a blocking capacitor C118 and a series grid resistor R130. The junction of C118 and R is connected to a 4.5 v. terminal through a grid return resistor R132, and the cathode is connected to this terminal through a resistor R134 having a capacitor C136 in parallel therewith. Plate current is supplied through a plate load resistor R138 connected to a B+ terminal. The plate is connected to a terminal 120 while the cathode is connected to a terminal 121 to provide signals of 0 and 180 phase, respectively.

Terminal 101 of the phase shift network is connected to the grid of a switching triode 140 through a decoupling resistor R142, and the output of triode 140 is coupled to the input of a triode 144 in the same manner that the triode 116 is coupled to the triode 110. The signal appearing at the plate of triode 140 and the signal at the cathode of triode 144 have a phase angle of 240 and these signals are impressed upon output terminals 123 and 124.

The terminal'102 of the phase shift network of the oscillator 90 is connected to the input of a triode which is coupled to a triode 152 in the same manner that the triodes 140 and 144 are coupled, and the output of the triode 152 is impressed upon the input circuit of a triode 154 which is similar to the triode 116 and is provided with similar circuit components. The cathode of triode 154 is coupled to an output terminal 125 while the cathode of triode 152 is connected to an output terminal 126. Since the signal on terminal 102 has a 90 phase, that appearing on the cathode of triode 152 Will be of 270 phase and the signal appearing on the cathode of triode 154 will be of 90 phase.

The terminal 103 of the phase shifting mesh of the oscillator 90 is connected to the input of a triode 160, the output of which is coupled to an amplifying triode 162. The output of triode 162 is coupled to the input of a triode 164 and the latter has its cathode connected to an output terminal 127. Since the signal at terminal 103 has a phase of 120 the signal on the cathode of triode 164 will also be of 120 phase.

It is not contemplated that'the vibrato oscillator and amplifying circuits of Fig. 2 shall be used in the form shown for any particular instrument. Instead, it is intended that this oscillator, and such of the amplifying apparatus as may be required for a particular instrument, be used and the remaining parts omitted. For example, the signals appearing on terminals 119, 120, and 123 are required only for the type of oscillator shown in Fig. 4. In many instruments it is necessary to have the vibrato frequency available in only two opposite phases so that the circuits associated with triodes 110 and 116 are the only ones that would be required and it would be necessary for the vibrato apparatus to have only two terminals such as 121 and 122 (in addition to a ground terminal) for such instruments.

The oscillator 90 preferably oscillates at approximately 7 cycles per second (c.p.s.) although in some forms of the invention disclosed herein it is required that several such oscillators be provided and that they oscillate at slightly different frequencies.

A similar pair of sources of frequency modulating signals may be derived from the apparatus shown in Fig. 2a and which may be employed in the manner above described with reference to the method diagrammed in Fig. 1a. In Fig. 2a triodes 92A and 92 are provided with phase shifting networks coupled to their grids in thesame manner as above described with reference to the oscillater of Fig. 2, with the exception that these networks have fewer sections to produce the required 180 phase shift. The outputs of the oscillator triodes 92A and 92B are suitably coupled to the input of switch tubes 94A and 94B. The switch tube 94A has its plate connected to a terminal 119A, which in a certain sense corresponds to the terminal 119 of Fig. 2. The triode 94B has a cathode resistor R95 and the signal across this resistor is utilized for frequency modulating the types of oscillators shown in Figs. 3 and 30, by having the V terminal of the oscillator connected to terminal 121A, which is connected to the cathode of triode 94B. The terminal 121A corresponds in general with the terminal 121 of Fig. 2.

Fig. 4 shows representative portions of a melody instrument, comprising an oscillator including a pair of triodes 170 and 71 driving a triode 172. The frequency of oscillation of this oscillator, is determined by a plurality of capacitors C176 connected between the grid of triode 170 and ground, and a plurality of inductance elements L178 which are connected in series between the grid of triode 170 and ground. The number of the inductance elements L178 which are effective is determined by switches 180 which are adapted to connect the junctions between successive inductance elements to a grounded conductor 181 upon operation of playing keys 183.

A number of coarse and fine tuning capacitors C182 are adapted to be connected between the grid of triode 170 and ground by means of switch members 184, initially to tune the instrument.

Whenever it is desired that the oscillator 170, 171 produce a vibrato, one or both of a pair of switches 186 is moved to its full line position, thereby eifectively to connect one or both of different value capacitors C187 between the grid of triode 170 and a conductor 189. The conductor 189 is adapted to be connected to terminal 119, 120, or 123 of the vibrato apparatus shown in Fig. 2, or to terminal 119A of Fig. 2a. It will be noted that these terminals are connected to the plates of triodes 110, 116, and 140 of Fig. 2, or triode 94A of Fig. 2a, respectively, and that these triodes operate effectively as a switch to connect conductor 189 substantially to ground potential and thus place one or both of the capacitors C187 effectively in the tuning circuit of the oscillator 170, 171 during substantially one half of each vibrato cycle. When the switches 186 are in dotted line position they connect compensating capacitors C185 in the tuning circuit of the oscillator and these capacitors have values respectively about one half those of the associated capacitors C187 so that when the oscillator 170, 171 operates without vibrato its frequency will be the average of the frequencies at which it operates under vibrato conditions.

In addition to operating the switches 180 the playing keys 183 operate switches 190 to connect a conductor 192 to ground, as will hereinafter appear. The wave front of the signal produced by the oscillator 170, 171 is made more steep by the triode 172 and is impressed upon a pulse sharpening and rectifying triode 194, the output of which supplies sharp negative pulses to the grids of alternate pulse responsive triggering triodes 196 and 197, which operate as the first stage of a frequency divider. Several cascaded stages of frequency divider circuits may be provided, each operating to divide the input frequency by two. Signals are derived from each of these stages as well as from the rectifier triode 172 and oscillator triode 170 through suitable coupling meshes which optionally may be connected to an output collector conductor 200 upon selective operation of switches 202 by stop tablets or the like. The signals appearing between the conductor 200 and ground are supplied to suitable tone quality controls 204, which may be in the form of a number of different filtering meshes, and the signal thus modified, in transmitted through transformer 206 in push-pull to the grids of a pair of control triodes 207, 208. These triodes are normally biased beyond cut off by having their cathodes connected through resistors R209 and R210 to a +250 v. terminal. Resistor R210 together with a resistor R211 form a voltage divider. The junction of these resistors is connected to conductor 192 so that when one of the switches 190 is closed the. potential on the cathodes of the control triodes 207 and 208 is reduced substantiallyto ground potential, and thus render these triodes conductive, the rate of attack and decay being controlled mainly by the values of R210, R211, C214, and C216. The control triodes 207, 208 are coupled by a transformer 218 to a power amplifier 220 which supplies a speaker 222.

Briefly, the section of an instrument shown in Fig. 4 operates in the following manner: Closure of one of the switches by depression of a playing key 183 higher than any previously depressed key will tune the oscillator 170, 171 to a frequency the same as or octavely related to the nominal pitch of the depressed key, and the several stages of frequency dividers will operate to provide frequencies successive octaves lower than that which the oscillator 170, 171 is tuned. After the closure of switch 180 the switch is closed to render the control triodes 207 and 208 conductive of the signal, with a suitable rate of attack and decay. Upon release of a depressed key its switch 190 opens to permit the potential on the oathodes of the control triodes 207 and 208 to rise to a cut oifvalue, and thereafter, upon opening of the switch 180, the oscillator 170, 171 will be tuned to its lowest frequency since all of the inductance elements L178 will be effectively in the oscillator tuning circuit. The family of tone qualities, as well as the pitch range desired, is controlled by selective operation of the switches 202 as well as by operation of the various tone quality controls 204. An over-all volume control of any suitable construction may be included in the input stage of the power amplifier 220.

Having described the construction and operation of most of the essential sections of electrical musical instruments, the manner in which the invention may be incorporated in complete instruments will now be described.

A very satisfactory type of instrument may be constructed in the manner shown in Fig. 5, wherein a melody section 230, which may be of the general construction shown in Fig. 4, is combined with a single manual organ section 231 comprising 37 oscillators of the kind shown in Fig. 3 or the kind shown in Fig. 3a. The melody section will have its conductor 189 connected to terminal 119 of the vibrato apparatus of Fig. 2 while the V terminals of all of the oscillators of the organ section are connected by a conductor 232 to the terminal 122 of the vibrato apparatus of Fig. 2. (As a less desirable alternative, the conductors 189 and 232 may be connectexl to terminals 119A and 121A, respectively, of the apparatus shown in Fig. 2a.)

All of the terminals F of the oscillators are connected to a terminal 234 while all the S terminals of the oscillators are connected to a terminal 236. Thus by operation of a switch 238 tone signals of the flute family will be supplied to a preamplifier 240 through a decoupling resistor R242, and similarly upon closure of a switch 239 tone signals of the string family will be transmitted to the preamplifier 240 through a resistor R243. The preamplifier 240 is coupled to a power amplifier 220 which supplies its output to a speaker 222. As in the previous instance the power amplifier may include a suitable volume control device in its input circuit.

It will be clear that in the instrument shown in Fig. 5 the signals produced in the melody section 230 will have a vibrato of 190 phase whereas the signals produced by the organ section 231 will have a vibrato of opposite polarity or 0 phase, and that as a result a rich chorus effect will be obtained when both sections are used at the same time. The chorus effect is most pronounced when the pitch, loudness, and quality of the solo and organ sections are the same. It will be understood that 11 the keys" of theorg'a'n section ordinarily will be des'ig'ned tooperate the key'switclies-of the melody section as-well as those of' the organ section:

The'invention'may be applied to an instrument'having but a single rank of generators o'r oscillators and this is accomplished as" Shown in Fig. 6. Inthi's instrument the oscillatorsfor' the first, third, and fifth" octaves will have their V terminals connected to terminal 121 of the vibrato apparatus; While the oscillators for the tones of'the even numbered octaves have their V terminals connected to the terminal 121 of the vibrato apparatus. These oscillators may be either of the type shown in Fig; 3 or the type'shown' in Fig. 3a andthe instrument is provided with the usual manual controls, amplifier, and speaker indicated by the block 250'. By thus connect in'g alternate octaves to oppositely-polarizedterminals of the vibrato apparatus many of the advantages of the invention are obtained,- althoughthe'underlying principles of the'invention are not utilized to the maximum extent. In an instrument such as shown in Fig. 6 the fundamental frequency ofa tone in-one octave will have its vibrato oppositely phased withrespect to thesecond harmonic of a tone an octavelower in the musical scale. Since the second harmonic is'of substantial intensity inmost musical tone qualities, and'since the fundamental frequency of the higher octave note is'ofthe'same', or substantially the same pitch as the second harmonic ofthe lower octave note, a very'pronounced chorus effect will be produced by these two generators because their vibratos'are oppositely polarized. In a large proportion of music'the' octave intervals appear frequently, so that the use'of theinvention in the manner shown in Fig. 6 is of substantial value in greatly improving the over-all musical results by the addition of the chorus'eifect.

A very desirable form of melodyinstrum'entmay be constructed by using two melody sections such as shown in Fig. 4, combining them in the manner'shown in Fig. 7. The first melody section 260 has its conductor 189 connectedto the terminal-119of the vibrato apparatus shown in 2 whereas the second melody section has its conductor 189 connected to the terminal 1200f the vibrato apparatus. The two sections may have-a manual 259 and a common output system 262. The latter includes the'variouscontrols, amplifier, and speaker. The tuning and control switches of both sections are operated by the keys of the single manual 2592 The chorus efiect in an instrument of this character is've'ry desirable because a musician can produce tones which are perceived by'auditors' as coming from a section of a symphonic orchestra. For example, by-using thestring tone qualities the'music'ian can produce musiccomparableto that pro-' duced by the'symphonic string section, and similarly, by an adjustment of the tone qualitycontrols, can'perform as a substitute for the horn section, the'oboe section, etc.

In-applyingthe invention'to a two manual instrument having two independent groups of oscillators for generating the tone signals the arrangement may be'of the type illustrated in Fig. 8; wherein block 266 represents an oscillator such as shown in Fig. 3 for the notes Cl and Clit; the 'block 267 represents the osc'illatorsfor the notes 'Dl to Bl; the block 268"tlie oscillators' for the-notes C2 to B2; the block 269-the oscillators for the notes 'C3 to B3; the block 270'the oscillators for the notes C4 to B4; and the block 271--the"oscillators for the notes C5 to B5.

It will'benoted that upon closure of switches 274 and 275," by' means of asuitable control tablet 276, the V terminals ofalternate octaves of oscillatorswill be connected to the terminal 122 of'the vibrato apparatus while'the intermediate' 'octaves of oscillators will have their'V'terminals connectedto the terminal 121 of the vibrato apparatus. Similarly the oscillators and genra; tor's' for the lower manual, upon closure ofswitches 278 and 279' 'by tablet '280," will have the V terminals of alte'rnate'octaves of oscillators connected to-the terminal 12 121 or the vibrato apparatus and the oscillators of the intermediate octaves will have their V terminals connected to the terminal 122 of the vibrato apparatus. Upon depression of a key such, for example, as- C1, switch 282' closed thereby will connect the'K terminal of the'oscillator'; such as shown in Pig. 3 to a B+ terminal thus supplying plate current to render the oscillator operative'. The C1 key, in addition to closing a switch 282 to render the oscillator operative, closes a switch 284 thereby connecting the T3 terminal of the oscillator to its S terminal and, by including the capacitors C58, C; and C62; (Fig. 3') in'the'oscillator tuning circuit, decreases the pitch at which the oscillator'operates by one semitone. When the tablets 276 and 280 are not depressed the switches operated thereby connect the V terminals to ground. I

If an oscillatoris provided for each pair of adjacent semitones a switch such as 284 must be provided to tune the-oscillator a semitone lower thanits normal frequency of oscillation, whereas if an independent oscillator is employed for each semitone the keys needto'operate only one switch such as the switch 282.

In an instrument of the type shownin Fig. 8 all of the terminals of all oscillators may be connected to a common conductor 286 and all of the S terminals connected to a common conductor 288. The conductor 286 is adapted to be connected to various tone controls 290 uponclosure of a fiute tone selecting switch 292, while if string quality tones are desired a switch 294 is closed. It will be noted that the conductor 288 is connected to ground through a relatively low value resistor R296 and is connected to the switch 294 by a mesh-comprising a series capacitor C295 and resistor R296, the latter having a capacitor C297 in parallel therewith. In a similar manner the output of all of the oscillators for the lower manual are supplied to suitable tone controls 299, the signals as modified by the controls 290 and 299 being supplied to preamplifier 300 which feeds a power ampli fier 302, the latter including an over-all volume control and supplying signal to a speaker 3%. v

In the instrument shown in Fig. 8 playing of octave notes on either manual results in the production of the chorus eirect between the fundamental of the higher note and the second harmonic of the lower note. If unison notes are played on both manuals the two tones produced will also have oppositely polarized'vibratos and the chorus effect will result.

The advantages of the invention may be obtained in the instrument shown in Fig. 9, but at considerable cost. In this instrument there are two'sets of master oscillators 310 employed to provide a controlling signal to cascaded frequency dividers 312, for example, in the manner disclosed-in the patent to Laurens Hammond 2,126,682 granted August 9, 1938. Any other suitable circuit arrangement may be employed in which master oscillators control the frequency of a series of dividers'extending through a range of four or five octaves, to provide the tone signals for the manuals and pedals. The outputs of these frequency dividers, under the control of the usual manuals and pedals is supplied to box 314 which represents the preamplifier, tone quality, volume, and reverberation controls, the power amplifier, and the speaker. I

The master oscillators 310 may be of any suitable construction but herein will be assumed to be of the type shown in Fig. 4, each having an input conductor 189 for connection to a vibrato switch tube. The conductors 189 forone groupor set of masteroscillators are connected to terminal119 of the vibrato apparatus of Pig. 2 whereas the conductors I39 or the second group of: master oscillators are connected to the terminal 12%} of the vibrato apparatus. If the master oscillators are of a type'in which the vibrato effect is obtained by impressing a vibrato frequency upon the control gridstas for example the oscillator in Fig. 3) then the Vterniinals of such oscillators should be connected to terminals 121 and 122. of thevibrato apparatus.

The key operating switching means of the instrument shown in Fig. 9 is such that, a signal from each group of master oscillators or each group of frequency dividers is transmitted to the output system upon operation of a single key. Thus depression of any key will result in the transmission to the output system of two signals of the same pitch (and preferably of the same or similar quality) but having oppositely phased vibratos, and as previously explained, this will be perceived by the listener as a rich chorus tone.

While the application of the invention to an instrument of the type employing master oscillators and cascaded frequency dividers requires substantial duplication of the tone signal generating apparatus, this additional cost is well justified by the greatly enhanced beauty of the music capable of being rendered, due to the addition of the chorus effect.

The invention may also be applied to very large and complicated organs employing several ranks of tone signal generators for each manual. Such an'instrument is diagrammatically represented in Fig. as having four six-octave ranks of generators for each of the manuals. The octave groups 320 of tone signal generators are connected to different terminals of the vibrato apparatus in a manner to produce a maximum chorus effect.

The generators of the signals used mostly on the upper manual are indicated as Diapason, 8', f; Cornopean, 8, mi; Salicional, 8', mp; Violin, 4', mp. The generators of tone signals used mostly on the lower manual are indicated as Open Diapason, 8', ff; Chimney Flute, 8, m); Harmonic Flute, 4, my; Dulciana, 8', pp.

The Diapason, 8, f has the V terminals of its odd numbered octaves of generators (assuming the generators are oscillators of the form shown in Fig. 3a) connected to the terminal 121 of 180 phase while its even numbered octave groups 320 are connected to the terminal ,122 of the vibrato apparatus of 0 phase. The Cornopean rank has the vibrato terminals of its odd numbered octave groups connected to terminal 122 and its even numbered octave groups connected to terminal 121 so that, for example, if the Diapason and Cornopean stops are used at the same time the signals provided by these ranks of generators will be modulated in opposite phase.

The Salicional, 8, mp rank has even numbered octave groups connected to terminal 125 (90 phase) while the vibrato terminals of its odd octaves are connected to the terminal 126 (270 phase). Thus if the octave notes are played using the salicional rank the vibratos on the two notes will be oppositely phased, and a chorus effect obtained between the second harmonic of the lower note and the fundamental of the higher note.

The rank of generators for producing violins, 4', mp,

have their corresponding octave groups of generators modulated in opposite phase with respect to the salicio-nal groups so that if these two ranks of generators are employed simultaneously an excellent vibrato chorus will result. Also because the successive octave groups of generators of the violin, 4 rank are modulated in opposite phase a certain degree of vibrato chorus will result'in the manner above explained. p The open diapason, 8, ff rank of generators have successive octaves provided with oppositely phased vibratos by having their vibrato terminals connected to the terminals 122 and 121 of the vibrato apparatus of Fig. 2, while the chimney flute, 8', m1 has its octave groups of oscillators phased oppositely to those of the open diapason.

Similarly the harmonic flute, 4', my rank of generators has its successive octaves oppositely phased by having their vibrato terminals connected to terminals 122 and 121 of the vibratoapparatus. The dulciana, 8', pp rank has alternate octave groups of generators connected to 14 terminals and 126 of the vibrato apparatus thus making the vibrato on adjacent octave groups of opposite phase.

By thus phasing the vibratos impressed upon the various octave groups of generators, it is highly probable that the organist will select generators from different ranks which are oppositely phased or which at least are not in phase. In this way the advantages of the chorus effect are obtained when playing with the more commonly used registrations and are attained in a large measure even when unusual registrations are employed by the organist, or when but a single rank of generators is being used.

As fully explained in the patent to Laurens Hammond No. 2,276,389 there are advantages in utilizing different vibrato rates on the tone signal generators for the twelve semitones of the musical instrument, so that when a chord is played the different notes will not rise and fall in frequency at the same rate and thus the undesirable effect of over-all vibrato periodicity is obviated. But the instrument described in said patent all octavely related notes were vibrato modulated at the same rate and in phase so that no chorus effect could be obtained between the second harmonic of the lower note and the fundamental of the note an octave higher in the scale.

The desirable vibrato chorus effect may be obtained while retaining the advantages of this invention by employing the apparatus shown in Fig. 11 wherein different generators 330 are controlled by vibrato modulating frequencies of various rates. The vibrato apparatus of Fig. 2 may be duplicated except for slight changes in the circuit constants so that one vibrato apparatus 332 will provide a modulating signal of 5.5 c.p.s., the next vibrato apparatus 333 operates at 5.8 c.p.s., and the vibrato apparatuses334 to 337 producing vibrato modulating signals at 6.1, 6.4, 6.7, and 7.0 c.p.s. respectively. Adjacent semitone generators 330, which are seldom used at the same time, are connected to the same terminal of one of the vibrato signal producing apparatuses 332 to 337. For example, generators 330 for the notes C1 and Clit are connected to the terminal .121, generators for notes D1 and D11? connected to the terminal 121 of a second vibrato apparatus 333, the generators for notes E1 and F1 connected to the terminal of vibrato apparatus 334 etc. The next octave of generators, for example, the generators 330 for the notes C2 and CZIF are connected to the terminal 122 of the vibrato apparatus 332 so that these generators will have their vibrato oppositely phased with respect to the generators an octave lower. The third and fifth octave generators would be connected in the same manner as the lowest octave generators while the fourth and sixth octave generators would be connected in the same manner as the second octave generators. The generators 330 may be keyed in the manner shown in Fig. 8 and may have their outputs transmitted to the output system in the same manner as shown in said figure, or in any other suitable way.

In a simple type of organ having but one set of generators the vibrato modulating frequency may be employed to obtain some chorus effect in the manner indicated in Fig. 12, wherein the first, third, and fifth octave groups of generators 340 have their vibrato terminals connected to the terminal 121 of vibrato apparatus 342 generating a vibrato frequency of 5.5 c.p.s., whereas the intermediate octave groups of tone generators have their vibrato terminals connected to a terminal 121 of a vibrato apparatus 343 operating at 6.5 c.p.s. The vibrato aparatus 342 and 343 may be identical with that shown in Fig. 2 except that the constants will be such as to produce the slightly different modulating frequencies. While the use of different vibrato rates, as illustrated in the examples of Fig. 12, is not as satisfactory as having the vibratos of the same rate but of opposite phase, this arrangement nevertheless utilizes in a substantial measure the underlying principles of the invention 15 because at particular instant there will usually be a substantial number of partials of the tones which are sharp relative to the nominal frequency and another sub stantial number which are flat relativeto the nominal frequency, thus producing a substantial chorus effect.

The invention may be embodied in an instrument of relatively low cost in the manner shown'in Fig. 13, where in' the oscillators are of the type shown in Fig. 3 capable of generating any one of four adjacent semitone frequencies. In Fig. 13 the oscillators 350, of the type of Fig. 3, are shown as each capable of providing the four adjacent semitone'signals except for the oscillators at the ends of the keyboard which need to cover ranges of only one, two or three semitones. The oscillators are under the control of keyfs354, each of which operates three or four switches including at least one switch 355 and one switch 356 for connecting the keying terminals K of adjacent oscillators 350 to a B-I- terminal and including at least streaming switch 358 to connect one of the terminals T1, T2, or T3 to either a' conductor 359 or conductor 360, thereby to tune one or two adjacentoscillators to the required, frequency.

The'frequencies capable of being generatedby the vari ous oscillators 350 are indicated in the drawing by the noteidesignations. By tracing the circuits it will be observedthat depressionof any key results in causing two adjacent oscillators 350 to, generate notes of the same pitch, and that such two adjacent oscillators whicl'i are capable of producing tone signals of the pitch calledfor by an operated 'k'ey, also have their K'terminal connected totheB j-terminal so as to 'render'therii operative. The vibrato terminals of alternate oscillators 350, are con nected to the terminal 121, and the; intermediate oscillatorsfare' connected to the terminal 122, of 'the vibrato apparatus of Fig. 2. Thusywhenever ajkey isdepressed, two adjacent oscillators will be; rendered operative and these two adjacent oscillators will have vibratos of op'posite phase impressed thereon so as to produce a full chorus eifect. v V V The' S terminals of all of the oscillators are connected toconductor 3 6 2 (to which condu'ctors 359 and 360are also connected) while the F terminals of' all the'bscillators are connected to 'a conductor 364 Under the"con'trol or optionally operable switches 366 and 367 tone signals" of desired string-like or flute-like quality, or both, are transmitted to the output'system. In Fig. 13 the output system isillustrated as comprising tones controls 368 coupledto a preamplifier 370 which transmits thesignals to a power amplifier 372 for energizing a speaker 374. e e I The invention may be incorporated in an organ having conventional coupler switching mechanisms between the manualsand the generators, such type of instrument being represented inFig. l4 as having an upper manual 380 and a"lower manual'382 each being capable ofbeing cou-' pled to: one or both sets of signal generators 384 and 386 by operation of' coupler switch mechanisms 388. In addition the upper manual maybe arranged'to control the sounding of a melody tone signal generator 3 90 of the "type shown in Fig. 4. The generator sets 384,386; and 390'mayeach have individual tone and volumecontrols '392 'coupling their outputs respectively to an over all volume control and arnplifier 394, feeding into a speaker 396.'

The chorus 'elfect is obtained in the'instrument shown in Fig." 14 by connecting the vibrato terminals V of the odd'numbe red octave groups of generators 384 to terr'ninal 122" phase) of the vibrato apparatus while the corresponding vibrato terminals of the even numbered octave groups are connected to thetenninal 127 (120 phase) of 'the'vibrato apparatus. The set ofgenerators386 are connected to the vibrato apparatus infamanner exactly opposite to: the generators384 "while 'the conductor 189 ofjjthe'melody tone signal generator 390 isconnected to the terminal 123' (240 phase) of 'the'vibrat o'apparatus' of Fig. 2. Thus'the three-tone signal generating sections of the instrument are in 0", and 240 phase relation withrespect to their vibrates and the instantaneous frequencies of signals of the same nominal pitch pro duced by .these' three sets of generators 384,386, and 390 will therefore be of the character indicatedby the curves of Fig. 16in which the full line curve 397 indicates a tone having vibrato phase of 0, the dotted curve 398' indicatesthe instantaneous frequency of a generator having a vibrato phase of 240, and the dash line curve 399 indicates the instantaneous frequency of a generator having vibrato phase of 120. From the curves'of Fig. 16' it will be clear that a large number of diiferent frequencies'will' be'present whenever tones of the same pitch frorri the three sets of generators are simultaneously pro-- duced and that when thctwo'sets' of generatorsare'played at' a'time the vibratos thereon will be sufliciently out of phase to produce a considerable chorus etfect.

In the various embodiments of the invention previously describedthe' chorus effect is obtained by modulating'two or more tone signals of substantially the same pitch or octavely related pitch by signals of the same frequency which are out of phase, or by two or more" signals of slightly different frequencies. The chorus effect according to the present invention may however beobtained from but'a'single musical tone'signal'source by utilizing" apparatus'of the'kind' illustrated in Fig. 18.

In thisfigure any source 400 of electrical'mu'sical tone signals which is deficientin' vibrato 'or' chorus,' or both, hasits'ou'tput coupled to'an artificial transmissionline generally in the manner disclosed in my prior Patent No. 2,382,413, but the artificial line usually need not be as long as' was desired for the apparatus shown in saidpatexit." The transmission line herein is shown as comprising seven series inductance elements L401 and six shunt capacitors' C402 which respectively connect the junctions 404 to :409 to ground. The line is shown as terminating in a suitable impedance R412. v,

Each of the junctions 404 to 409 is connected to two capacitor plates 414 which'are adapted to' be scanned by scanner plates 416and 417, suitably mounted on a shaft 438," 180 apart. The connections between the junctions 404 to 409 and the plates 414 are such that as the plates416 'and 417 are rotated at a constant speed they respectively scan to and fro along the line, all as more fully disclosed in said prior Patt nt No. 2,382,413. The signals appe'aring on thescanner plates 416 and 411m transmitted through slip ring'conneetions (not shown) to amplifiers 418 arid .419 having their outputs coupled to speakers 420 and 421.1 I e u p The scanner plates 416 and 417 are rotated at a suit able vibrato speed, e.g.' 7 revolutions per second, and thu's'th'e signals picked 'up by them have vibrates introduced therein 'inpha'se oppositionto produce the chorus effect. To prevent the production of undesirable tremulaiit effects andcancellation or partial cancellation of thej'two" signals appearin'gfon the scanner plates 416 and 41 7 they are amplified by separate amplifiers and trans lated into sound by'sepa'rate sepakers. The reasons that this is 'd'esirablefare more. fully set forthin my copending application Serial No. 276,73 1, filed March 15, 1952, 110 Patent No. 2,830,481. It may be statedhere, however, that by virtue of theisepar'ation of the xsignalsjuntil they are translated 'into sound,' they add acousticallyif in a room' having soundjrefiecting walls, whereas, if they were' combined' electric'allythere would be a noticeable, irregular and undesirable tremulant effect. The appa ratus of {Fig 18 thus provides 'rneansj'for -converting a single musical tone signal into a chorus'of signals with the astonishing results heretofore described.

Upo'ii'occ'asion it may be desired to utilize the artificial" line'vibrato apparatus of saidPatent No. 2,382,413 in conjunction with an organ tone signal generating'sysr tern which does not produce tones with the vibrato and also to employ With said organ a melody section." The 

